The Lightroom 1.4 update has been temporarily removed from the Adobe.com web site in order to allow time for additional investigation into several bugs that were discovered after the update was released. At this time, we recommend uninstalling Lightroom 1.4 and installing Lightroom 1.3.1.

This advice applies to both the Windows and Mac versions. You can read more in the Lightroom Journal including an apology from the development team.

Bizarre, I got my update on the day it came out with no problem. And I've just checked now and it's available for download and I just downloaded both the mac and windows updates. Let me know if you want me to send the updates to you.